Methods whereby heat energy, and particularly waste heat energy, is transformed into useful mechanical energy by vapor power (Rankine) cycles is well known. The basic method comprises causing a suitable working or power fluid to pass in heat exchange relationship with a source of heat of sufficient intensity to vaporize the fluid; utilizing the kinetic energy of the expanding vapors to perform work by passing them through a turbine machine or other work producing device, condensing the vapor and pumping the condensed liquid back in heat exchange relationship with the heat source to complete the cycle.
A variety of fluids have been tested in the past as power fluids for this type of application. Water or steam has been the most commercially utilized power fluid. However, the high boiling point, high critical pressure and low density of water or steam limit the power obtainable and result in a need for relatively large and bulky apparatus with these fluids.
A number of organic liquids have been tested as power fluids (e.g. U.S. Pat. Nos. 2,301,404; 3,162,580; 3,234,738; 3,282,048; 3,516,248; and 3,511,049), but there has not been found any single fluid suitable for use as a power fluid which possesses, to the optimum degree, all of the important properties of being thermally stable at elevated temperatures, non-corrosive to ordinary materials of construction and possession of a high Rankine cycle efficiency.
In the development of Rankine cycle systems, the need exists for improved fluids possessing advantageous combinations of properties for Rankin cycle applications, particularly contributing a high Rankine cycle efficiency to the system.
Since no single fluid has been found which is ideal for Rankine cycle applications, the art has turned to the preparation of blends or mixtures of fluids which give novel combinations of properties for Rankine cycle and other applications.
Blends of 1,1-difluoroethane and monochloropentafluoroethane have been evaluated as refrigerants (World Refrigeration, February and March 1957), but such blends do not possess a desirable combination of properties for Rankine cycle applications. Blends of 1,1-dichloroethane and 1,1,2-trichlorotrifluoroethane are also known (Canadian Patent No. 832,341), but likewise do not possess a desirable combination of properties for Rankine cycle applications.
Non-constant boiling blends are candidates for Rankine cycle applications, however, non-constant boiling mixtures suffer from the disadvantage that they fractionate during use and during reclamation thereby losing to a greater or lesser extend, one or more of the more volatile components, thereby changing the relative proportion of the components and hence, the properties of the mixtures. The changed properties may be less advantageous from the standpoint of Rankine cycle applications.
The above described problem with non-constant boiling mixtures does not exist with constant boiling (or azeotropic) mixtures. Unfortunately, however, although azeotropic mixtures are advantageous for this reason, as evidenced by the disclosure in U.S. Pat. No. 3,085,065 to Kvalnes, a reliable basis has not been found for predicting the formaton of azeotropes, particularly among halocarbons.
It is an object of this invention to provide a novel fluid mixture which has utility in Rankine cycle applications.
It is another object of this invention to provide novel constant boiling compositions which have application in Rankine cycle systems.
It is another object of the invention to provide constant boiling compositions which have high Rankine cycle efficiencies when used as working fluids in such systems.
Other objects and advantages of the invention will be apparent from the following description.